1. Field of the Invention
The present invention relates to a power management apparatus and a power management method for managing a power supply that supplies power to an electric device. In addition, the invention relates to a power management system including the power management apparatus.
2. Description of Related Art
Conventionally, a power management apparatus for supplying power to an electrical device has a function of automatically (or manually) switching to a power saving mode for suppliance of a minimal necessary power when the electrical device is inoperative for a predetermined time. Thereby, unnecessary power consumption is reduced, and consequently, resources can be conserved.
When the electrical device is in the power saving mode, the suppliance of power can be returned to a normal mode using a return signal input according to a user's desire.
In the conventional electrical device, even when the suppliance of power switches to the power saving mode, power is continually supplied to a driving control circuit mounted in the electrical device, and the return signal is monitored. Consequently, management control can be implemented so that the switch operation for switching the suppliance of power to the power saving mode and the return operation for making the suppliance of power return to the normal mode do not temporarily overlap.
However, the continual suppliance of power in the power saving mode to the driving control circuit of the electrical device conflicts with an intrinsic purpose of the power saving mode for reducing power consumption. To overcome this problem, in recent power management apparatuses, the suppliance of power to the driving control circuit is cut off in the power saving mode (or, system shutdown is caused). An electrical device used in this case has a compact complex programmable logic device (CPLD) in addition to the driving control circuit. The CPLD is continually supplied with power even in the power saving mode, and executes return control upon receipt of a return signal.
Nevertheless, in the operation of making the suppliance of power return from the power saving mode, a power-saving power supply is controlled by transistor-switching operations, and control is thereby performed for a device to which the suppliance of power has been cut off. Accordingly, the voltage of the power-saving power supply gradually rises. Consequently, a case can occur, in which the voltage of the power-saving power supply drops temporarily because of a rush current until the voltage reaches an operation-guaranteeing voltage (voltage at which the suppliance of power from the power-saving power supply is stabilized). This can cause a case, in which this device produces an uncertain signal.
A case can occur, in which the uncertain signal is input to a device, to which power is continually supplied even in the power saving mode, causing this device to operate erroneously. In particular, when a shutdown signal is input to the CPLD because of the rush current, a case can occur, in which the return operation and shutdown operation are repeated, whereby the suppliance of power cannot be returned to the normal mode.